The present invention relates to a motor speed control system and in particular to a signal translator which enables a speed control generating output signals within a first range of voltages to be used with prior art speed regulators that operate from control signals within a second range of voltages, where the second range of voltages may vary from one model of speed regulator to another.
The prior art includes speed regulators that may operate as either AC or DC and may be SCR or AC inverter drives. Such prior art speed regulators typically include a potentiometer to which a reference potential is applied that is within a certain range of voltage, and where the voltage at the variable tap is used to regulate the motor speed. Such speed regulators are well-known and conventional and may have been operating in certain existing speed control systems for many years.
The prior art also includes speed controls, in particular digital speed controls, with a manual or automatic means for selecting a desired motor speed and means for generating an electrical signal corresponding to the selected speed. The prior art speed controls are provided with a feedback signal that is representative of the actual motor speed. The output of the speed control may fall within a range of voltages that is not compatible with the range of input control signal voltages of the speed regulator. Therefore, in order to incorporate the improved speed controls in prior art systems with conventional speed regulators as described above, one must completely redesign the motor speed control system or undertake extensive engineering modifications of the speed regulator such that it is compatible with the speed control. Since the prior art speed regulators and speed control systems are quite expensive there is reluctance undertake such extensive rework or redesign.
The present invention solves this problem in the prior art by providing a signal translator which enables digital speed controls which operate in a first range of output signal voltages or currents to be used in combination with existing prior art speed regulators that operate within a second range of input control signal voltages, without need for any voltage scale adjustments or readjustments. The present invention thus permits the utilization of the improved and more efficient speed controls in existing motor speed control systems, without requiring expensive engineering modifications.